Things you need to know

This dataset is published with the Using statistical models to estimate UK international migration Methodology Working Paper.

Important information for interpreting these modelled estimates:

1. Multivariate State Space Models (SSM) are used to estimate international migration using administrative outcomes data

2. Data sources included in our models:

• International Passenger Survey (IPS) monthly estimates of immigration and emigration, UK, January 2010 to February 2020
• Home Office (HO) border crossing data, Visa and Advanced Passenger Information data, UK, April 2015 to October 2020
• Civil Aviation Authority (CAA), Train and Ferries data, UK, January 2010 to September 2020. These were the data available at the time we developed our models.

Modelled estimates

1. We use expert judgement on model assumptions to produce a range of provisional modelled estimates for the coronavirus period

2. Estimates are generated from the models for British, EU and non-EU nationals’ immigration and emigration and are summed to estimate the corresponding totals. Net migration is calculated by taking the difference between immigration and emigration.

3. Monthly IPS estimates and uncertainty intervals for January 2018 to February 2020 are presented in the Data tab. Modelled estimates and uncertainty intervals are presented for March 2020 to June 2020.

4. Uncertainty intervals around these modelled estimates emphasise that it is not possible to accurately quantify international migration in this unprecedented period with a single point estimate. Please refer to Appendix 1 in our Methodology Working Paper, Using statistical models to estimate UK international migration for further information on estimating uncertainty.

5. The uncertainty intervals for net migration are calculated using the sum of the prediction error variances derived from the immigration and emigration confidence intervals. They should be treated as indicative; in future iterations we will develop a more precise measure which will not necessarily be symmetrical around the estimated net migration values.

6. Please refer to Appendix 1 in our Methodology Working Paper Using statistical models to estimate UK international migration for further detail on the mathematical specification of the multivariate State Space Models

7. These modelled estimates are provisional as our models develop and will be subject to retrospective confirmation and adjustment as data become available or mature

Assumptions underpinning our models

Our assumptions are based on empirical evidence and expert input from a Delphi approach. Implemented assumptions for the immigration and emigration models following expert advice are:

Immigration

• Non-EU: Model from March 2020
• EU: Model from March 2020 but apply travel options adjustment from April 2020
• Great Britain: Model from March 2020 using non-EU Home Office border crossing data on departures

Emigration

• Non-EU: Model from March 2020
• EU: Model from March 2020 but apply travel options adjustment from April 2020
• Great Britain: Model from March 2020 using non-EU Home Office border crossing data on arrivals

Notes:

1. Modelled estimates are based on the UN definition of an international migrant. That is a person who moves to a country other than that of his or her usual residence for a period of at least a year (12 months), so that the country of destination effectively becomes his or her new country of usual residence
2. Refugees and asylum seekers are excluded from modelling
3. The monthly estimates of international migration flows have been derived solely for the purpose of this research and should not be treated as official statistics or used in any other context

Feedback

We welcome feedback from users, please contact Vital Statistics Outputs Branch email: demographic.methods@ons.gov.uk

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